1. Field of the Invention
This invention relates to a forming press apparatus for bending a trimmed workpiece.
2. Description of the Related Art
FIG. 7 hereof shows a typical vehicle body panel forming line of related art. This forming line is made up of three specialized machines: a drawing machine 100, a trimming machine 103 and a bending machine 106.
The drawing machine 100 has a drawing die pair 102 fitted to a press 101. The drawing die pair 102 consists of an upper die 102a and a lower die 102b. The trimming machine 103 has a trimming die pair 105 fitted to a press 104. The trimming die pair 105 consists of an upper die 105a and a lower die 105b. The bending machine 106 has a bending die pair 108 fitted to a press 107. The bending die pair 108 consists of an upper die 108a and a lower die 108b. 
An example of forming a vehicle body panel with these specialized machines 100, 103 and 106 will now be described.
First, a blank is set in the drawing die pair 102 of the drawing machine 100. Then, the press 101 is operated and the blank is drawn. By this means, a drawn forming 110 is obtained.
Next, the drawn forming 110 is set in the trimming die pair 105 of the trimming machine 103. The press 104 is then operated and the edge 110a of the drawn forming 110 is trimmed off. By this means, a trimmed forming 111 is obtained.
The trimmed forming 111 is then set in the bending die pair 108 of the bending machine 106. The press 107 is then operated and bending is carried out on the edge 111a of the trimmed forming 111. By this means, a bent forming 112 is obtained.
Finally, various holes are made in the bent forming 112 to produce a vehicle body panel, and the vehicle body panel is assembled to a vehicle body on an assembly line.
In this way, a method has been typically employed wherein to manufacture a vehicle body panel at low cost wherein the vehicle body panel is mass-produced using three separate specialized machines like the drawing machine 100, the trimming machine 103 and the bending machine 106.
However, in recent years there has been a trend for car model changes to be made in relatively short cycles, and there has also been a change from the mass production of a few product types to the smaller-volume production of each of numerous product types. In the case of this high-variety, small-volume production, if three specialized machines like the drawing machine 100, the trimming machine 103 and the bending machine 106 are provided separately in a vehicle body panel forming line, the cost of the plant cannot be recovered and it is difficult for the cost of the vehicle body panel to be kept down.
In this connection, in U.S. Pat. No. 4,625,540 there is disclosed a press apparatus wherein a plurality of forming die pairs corresponding to a plurality of forming steps are mounted to a single press, and drawing is carried out at a first working station, piercing and finishing are carried out at a second working station, and trimming and splitting are carried out at a third working station.
However, when an upper/lower pair of dies for drawing are mounted in a row with other dies in the same press, because of the need to lay out cushion pins and the like for carrying out drawing from a flat sheet workpiece, inevitably the press itself becomes large.
And also, when a flat sheet workpiece is to be formed into a three-dimensional shape, because the forming load of the drawing step of the first working station is larger than the forming loads of the second and third working stations, the second and third working stations exert locally high loads. Consequently, the press as a whole becomes load-imbalanced, and the overall balance of the press may not be optimal for carrying out pressing in one shot.
It is therefore an object of the present invention to provide a forming press apparatus with which product cost can be kept down; which is not overly large; and which as a whole does not become load-imbalanced during pressing.
To achieve this and other objects, the invention provides a press apparatus for manufacturing a forming by press-forming a workpiece in a plurality of successive forming steps, which comprises a single press and die sets mounted raise/lowerably to the press and carrying en bloc a plurality of forming die pairs corresponding to the plurality of forming steps, wherein the plurality of forming die pairs include a primary forming die pair and a secondary forming die pair so that the plurality of forming steps are carried out simultaneously.
A primary forming is carried out on a metal sheet workpiece with the primary forming die pair in one shot of the press, and then the workpiece is transferred to the secondary forming die pair and a primary forming and a secondary forming are carried out simultaneously in the next shot.
Preferably, the plurality of forming die pairs are disposed in a row on the die sets in the order of the forming steps.
Thus, in this invention, because a plurality of forming die pairs of differing types are provided en bloc on upper and lower die sets on a single press, only one press is required for the plurality of forming steps; a plurality of die pairs can be moved simultaneously; and forming of a plurality of different workpieces can be carried out at the same time. In particular, because the forming of workpieces is carried out after drawing, which involves a large forming load, even when simultaneous forming is carried out with a single press there is no load-imbalance, and a well-balanced load can be applied to the plurality of die pairs.
The plurality of die pairs may preferably include a trimming die pair for trimming a pre-drawn forming, a coarse bending die pair for carrying out coarse bending on the trimmed forming obtained, and a finish bending die pair for carrying out finish bending on the coarsely bent forming obtained.
The stroke necessary for a trimming die and the stroke necessary for a bending die sometimes differ. Because normally the stroke of a bending die is larger than that of a trimming die, when a trimming die and a bending die are mounted on a single press, sometimes the stroke necessary for the bending cannot be provided and the required bent forming cannot be obtained; in this invention, however, two die pairs, a coarse bending die pair and a finish bending die pair, are provided as the bending die pair. Consequently, coarse bending can be carried out on the trimmed forming with the coarse bending die pair, and finish bending can be carried out with the finish bending die pair on the coarsely bent forming obtained. As a result, the workpiece can be bent in two stages and the workpiece can be bent to the desired shape.